A 9-year-old male neutered European Shorthair cat with a body weight of 4.8 kg and a body condition score of 6/9 was presented to the referring veterinarian owing to acute vomiting and a subjectively perceived mild weight loss. A blood examination by the referring veterinarian revealed a markedly increased concentration of total calcium (tCa) (15 mg/dl; reference interval [RI] 7.8–11.3 mg/dl), as well as a mild hypophosphataemia (2.5 mg/dl; RI 3.1–7.5 mg/dl). Haematology and the remaining biochemistry results showed no relevant abnormalities (mild hyperglycaemia attributed to stress and a mild hyperglob-ulinaemia of 5.4 g/dl [RI 2.8–5.1 g/dl]). The cat was referred for further investigation of hypercalcaemia. Physical examination 12 days later showed no abnormal findings and no cervical mass was palpable. A complete blood count was repeated, which showed normal values. Ionised calcium (iCa) concentration measured on site with a hand-held device (i-STAT; Abbott) showed an increased concentration of 2.19 mmol/l (RI 1.16–1.40 mmol/l) (). Biochemistry profile confirmed markedly increased tCa concentration (4.05 mmol/l; RI 2.20–2.90 mmol/l) and hypophosphataemia (2.6 mg/dl; RI 3.4–5.3 mg/dl). Plasma for PTH and parathyroid hormone-related protein (PTHrP) measurement was sent to an external laboratory (Alomed, Radolfzell, Germany) to investigate the cause of hypercalcaemia. Possible differential diagnoses for markedly increased concentrations of tCa and iCa combined with hypophosphataemia were hyperparathyroidism, hypercalcaemia of malignancy and idiopathic hypercalcaemia. Markedly increased PTH concentration >1000 pg/ml () and normal PTHrP concentration <0.5 pmol/l (RI <0.8 pmol/l) was consistent with primary hyperparathyroidism in this cat. Two days later, a cervical ultrasound was performed under intravenous propofol (Narcofol; CP Pharma) anaesthesia to look for a possible parathyroid mass. At this time, the owner reported polydipsia and polyuria over the past couple of days. The cat was positioned in dorsal recumbency and the region of the thyroid and parathyroid glands was clipped. Ultrasonographic examination was performed by a board-certified radiologist (AH) with an 18 MHz linear transducer (Toshiba applio400). Within the left thyroid gland a heterogeneous mass (size: 13 × 7 × 6 mm) with a mixed echogenicity was visible. The mass showed areas containing corpuscular fluid, as well as solid hypoechoic areas. Location of the mass was compatible with the caudal left parathyroid gland ( and ). The region was surgically prepared and an ultrasound-guided fine-needle aspiration of the mass was obtained with a 22 G needle. Afterwards, the amount of ethanol needed for chemical ablation of the mass was calculated based on earlier studies in dogs, where half of the mass volume was set to be the target amount of ethanol. Calculation led to a target amount of 2 ml of 96% ethanol, which was administered under ultrasound guidance, observing dissemination within the mass, with a 22 G needle attached to a 2 ml syringe. The ultrasonographic appearance of the gland and dissemination of fluid was recorded and a good blanching was ultra sonographically visible (). Owing to the high volume of ethanol, 0.23 ml (0.015 mg/kg IV) of buprenorphine (Buprenodale Multidose; Dechra) was injected intravenously as an analgesic. The cat was allowed to recover from anaesthesia immediately afterwards. Cytology showed neuroendocrine tissue but could not differentiate between benign or malignant tissue. Approximately 24 h and 72 h, as well as 5 days, 4 weeks and 4 months, after ethanol injection, the cat was re-examined and iCa concentration was measured. Furthermore, the owner was told to present the cat immediately should any clinical sign of hypocalcaemia occur, such as tetany, facial rubbing (pruritus), seizures or weakness. By 24 h after chemical ablation the iCa concentration was within the RI (). The owner reported normal general demeanour, no polyuria or polydipsia, and the cat was clinically normal and vomiting stopped. Similar findings were seen 72 h and 5 days after chemical ablation, except that there was a mild voice change and a mild prolapse of the nictitating membrane 4 days after the injection. Repeated measurements of PTH concentration were performed 5 days, 4 weeks and 4 months after the ablation (), which showed a gradual decrease of the hormone almost into the RI. Four weeks after chemical ablation, the cat still had a mild prolapse of the nictitating membrane and the voice change persisted, but both findings were no longer present at the re-examination at 4 months. PTH concentration was measured in a different laboratory (Cambridge Specialist Laboratories, UK) at the final re-examination due to a change in techniques in the initial laboratory reporting a slightly different RI (<40 pg/ml). Body weight 4 weeks and 4 months after ablation was 4.6 kg and 5.4 kg, respectively.